[vtkusers] Read PNG from in-memory buffer?

[Elvis Stansvik]

2016-09-29 13:42 GMT+02:00 Andras Lasso <lasso at queensu.ca>:
> You can use libpng directly (it's included with VTK). See how it is done in the PLUS toolkit:
> DecodePngImage(unsigned char* pngBuffer, unsigned int pngBufferSize, vtkImageData* decodedImage)
> https://app.assembla.com/spaces/plus/subversion/source/HEAD/trunk/PlusLib/src/PlusDataCollection/BkProFocus/vtkPlusBkProFocusOemVideoSource.cxx#ln549

Thanks for the pointer Andras. In my case I was interested in reading
the PNG from the Qt resource system, and I found the
vtkQImageToImageSource helper class which fits like a glove.

Had I not found it, I might have gone down the route of writing my own
VTK "from memory" reader class using libpng.

Elvis

>
> Andras
>
> -----Original Message-----
> From: vtkusers [mailto:vtkusers-bounces at vtk.org] On Behalf Of Elvis Stansvik
> Sent: September 29, 2016 7:32
> To: VTK Users <vtkusers at vtk.org>
> Subject: Re: [vtkusers] Read PNG from in-memory buffer?
>
> 2016-09-29 13:29 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>> 2016-09-29 11:35 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>>> 2016-09-29 9:29 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>>>> I'd like to read a PNG from an in-memory buffer. Looking at
>>>> vtkPNGReader, it seems it only works with files in the file system.
>>>> In general, is there some way to use the reader classes in VTK with
>>>> in-memory data, or would I have to write my own custom reader?
>>>>
>>>> My need for this is not great, I was simply hoping to be able to
>>>> keep this particular PNG in the Qt resource system (so in the end,
>>>> embedded in my executable), load it using Qt file facilities, and
>>>> use VTK on the read in-memory data.
>>>
>>> I realize now that I can probable use QImage to load/decompress the
>>> image, and pass the uncompressed data to a vtkImageImport, but I
>>> can't find any docs on what format vtkImageImport expects for the pixels.
>>> Anyone know?
>>
>> I had a go at this approach, using QImage::Format_RGBA8888 as I think
>> (?) that's the format vtkImportImage wants, but the resulting image
>> looks garbled when shown in VTK:
>>
>>     // Load image with QImage
>>     QImage image(":/images/orexplore-logo-80x47.png");
>>
>>     // Convert to RGBA8888
>>     image = image.convertToFormat(QImage::Format_RGBA8888);
>>
>>     // Have a look at the image to make sure it's OK
>>     auto debugLabel = new QLabel();
>>     debugLabel->setPixmap(QPixmap::fromImage(image));
>>     debugLabel->show();
>>
>>     // Import into a vtkImageData
>>     auto imageImport = vtkSmartPointer<vtkImageImport>::New();
>>     imageImport->SetDataSpacing(1, 1, 1);
>>     imageImport->SetDataOrigin(0, 0, 0);
>>     imageImport->SetWholeExtent(0, image.width() - 1, 0,
>> image.height() - 1, 0, 0);
>>     imageImport->SetDataExtentToWholeExtent();
>>     imageImport->SetDataScalarTypeToUnsignedChar();
>>     imageImport->SetNumberOfScalarComponents(4);
>>     imageImport->SetImportVoidPointer(image.bits(), 1); // Note:
>> QImage::bits() deep copies
>>     imageImport->Update();
>>
>>     auto mapper = vtkSmartPointer<vtkImageMapper>::New();
>>     mapper->SetInputData(imageImport->GetOutput());
>>
>>     auto actor = vtkSmartPointer<vtkActor2D>::New();
>>     actor->SetMapper(mapper);
>>
>> Anyone know exactly what format vtkImageImport expects, or, if it
>> expects RGBA (unsigned char), why the above won't work?
>
> Whoa. Just found
> http://www.vtk.org/doc/nightly/html/classvtkQImageToImageSource.html
> :) I'll of course use that. Sorry for the noise.
>
> Still interested in why the above approach wouldn't work, out of curiosity.
>
> Elvis
>
>>
>> Elvis
>>
>>>
>>> Elvis
>>>
>>>>
>>>> Elvis
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